This project examines platelets as models for the study of uptake, storage, and metabolism of serotonin and other biogenic amines in man. In particular, these studies have defined more critically the nature of the plasma-membrane uptake of dopamine, tyramine, serotonin, and serotonin analogs. Vesicular accumulation and binding of dopamine, octopamine, tryptamine, norepinephrine, tyramine, fluoro-substituted tyramines, serotonin, and serotonin analogs has been measured. The action of the tricyclic antidepressant imipramine to inhibit the uptake of serotonin into vesicles has been demonstrated. Oxidative deamination of tyramine, tryptamine, and serotonin has been evaluated in intact platelet cohort. Studies of platelet storage packet-size for serotonin, calcium, and phosphorus have revealed that vesicles are normally significantly undersaturated with respect to maximal serotonin binding capacity.